Update list of default empty elements
Ensure html_escape docs are picked up by Yard

Move documentation blocks for html_escape and escape_once next to the
respective method definitions for Ruby 1.9+ so that Yard correctly
includes them.
Update links in FAQ.md

Fixes #679
Explicitly join ambles in SafeErubisTemplate

Previously Tilt used `join` to combine ambles and template, which
flattened our arrays for us, but this changed in Tilt 1.4.

Return Strings from precompiled_preamble and precompiled_postamble.

Fixes #675
Use custom Erubis handler subclass for Erb filter

The Rails Erubis handler has added code to reduce the number of method
calls when adding newlines (see
https://github.com/rails/rails/commit/bd308a0d02c4a6459c05770a564405986a663f47).

This uses a new instance variable, which is initialised in the
add_preamble method. Tilt explicitly ignores the preamble from Erubis,
using its own, so this variable is never initialised. This causes
failures with the Erb filter when this variable is referenced.

By using our own custom subclass the variable can be initialised in the
classes initialize method, preventing failures.

Fixes #669
Add reference documentation of useful helper methods
Updated Changelog
Use https://rubygems.org